BACKGROUND Pulmonary metastasectomy is an accepted procedure in selected patients, very often requiring multiple non-anatomical resections. Although it is intuitive that functional loss is proportional to the number and extent of pulmonary resections, this link has never been proved and is the hypothesis behind this study. METHODS We retrospectively reviewed pulmonary function changes after lung metastasectomy. Baseline and postoperative spirometric values were evaluated and their changes were correlated to (a) number of resections, (b) extent of resections and (c) intervals between surgery. RESULTS Sixty-six patients were enrolled (31 men, mean age 56 years, range: 23-75); mean interval between surgery: 54.5 days; mean extent of resection: 11.45 cm; mean number of resections: 3. Preoperative mean spirometric values were: FEV1 2.73 l (97.75%); FVC 3.11 l (95.50%); DLCO/AV 1.21 l (99.80%). Mean changes in FEV1, FCV and DLCO/AV were -13.4%, -12.4% and +1.2% respectively. Patients receiving three or more non-anatomical resections had functional loss similar to those undergoing lobectomy. The extent of total resection (>11 cm, p<0.05) and the interval between surgery (>90 days, p<0.0001) influenced FEV1 and FVC modifications. At three months none of these functional modifications remained. Sex, age, side of the operation and histology of primary tumor did not affect spirometric changes. CONCLUSIONS Spirometric changes after pulmonary metastasectomy are affected by total volume lung parenchyma resected within the first 90 days. Functional loss after three or more non-anatomical resections is comparable to that recorded after lobectomy.